1. Field of the Invention
This invention is directed to a guide mechanism for guiding a stretch-wrap machine around material to be wrapped.
2. Description of the Prior Art
Modern mechanized handling requires that a number of small packages be packed together so that they can be handled in larger units. Pallets are used as a base, and packages are stacked on the pallet to a convenient size and weight for mechanical handling. One approach to retaining the packages on the pallet has been steel banding. Steel bands were placed around the packages and the pallet and the bands tightened and clamped. The problem with steel banding is that loads can shift, and under the wrong circumstances, all the packages on the outer extremities of the load directly under the steel bands can be crushed. Furthermore, the steel bands are difficult and dangerous to handle. Steel bands are most useful on heavy metal objects, such as pipe and other forms of steel. It must be noted that steel banding does not provide any weather protection for the packages.
A newer method of securing packages on a pallet to provide a palletized load is to shrink wrap the packages and the pallet. In this arrangement, bags are made out of shrink material (usually polyethylene), and the bag is placed over the palletized packages. Thereupon, the bag is subjected to heat whereupon it shrinks to unitize the palletized load. Shrink wrap is useful for loads which are of uniform size, but requires special equipment for causing the shrinkage. Since heat is used to cause the shrinkage, it cannot be used in cold rooms or other areas where high heat loads are objectionable. Furthermore, it cannot be used over polyethylene wrapped packages because of sticking between the shrink wrap material and such packages.
To overcome these disadvantages, stretchwrapping has been developed. In these machines, one of which is seen in Lancaster U.S. Pat. No. 3,867,806, a stack of packages is placed on a turntable. Usually, these packages are mounted on a pallet. The turntable is rotated, and the palletized load of packages is wrapped with a stretch-wrap material. This material may be polyethylene or polyvinylchloride web or film and is manufactured to be able to stretch at least 25 percent. During wrapping of the load, tension on the stretchwrap film provides a tension which stretches the film from about 15 to 25 percent. The film is thin, usually about 1/1000th of an inch, and the load is wrapped with as many thicknesses as is necessary to obtain the desired unitized load strength.
The stretch-wrap film may be as tall as the load or may be narrower than the height of the load. In the latter case, the narrower film is spiral-wrapped around the load. Since more wraps are necessary at the top and bottom of the load than at the middle for best strength, this is more economical of material. However, these stretch-wrap concepts have been limited to those loads which can be placed on the turntable and rotated.
U.S. Pat. No. 4,095,395 to Joseph Goldstein is directed to a stretch-wrap machine wherein a motive unit carries the stretch-wrap unit and wherein the motive unit is guided around the material to be wrapped. In this arrangement, the material to be wrapped is in a stationary position. This invention is directed to a guide ski assembly useful in such a self-guiding stretch-wrap machine and which is particularly arranged for guiding the stretch-wrap machine around uneven material loads.